This invention relates to fiber-containing, optionally cellular polyurethane moldings having inhomogeneously colored surfaces with color contrasts in fiber-like distribution and a process for their production.
It is known that moldings of cellular or non-cellular polyurethanes can be provided with a surface coloration by addition of pigments, dyes or both to the reaction components. It is also known that colored surfaces can be obtained by treatment of the moldings by immersion in dye baths, by spraying, by casting or by in-mold coating. One disadvantage common to these known processes is that addition of conventional coloring constituents to the liquid components gives a homogeneously colored surface which leaves the impression of a typical plastic surface. However, such a surface is not always desirable for articles such as fashionable shoe soles.
Inhomogeneously colored surfaces may also be obtained by color treatment after formation of the article (e.g., application of lacquers by spraying). However, this type of treatment involves greater expense and, in the case of integrally foamed shoe soles, for example, can only be applied after special measures (such as masking the upper part of the shoe by means of screens) have been taken. In addition, such application of lacquers results in a surface image which is being rejected to an increasing extent for reasons of fashion.
Fiber-filled polyurethane elastomers, particularly those based on chopped and ground glass fiber additions (see German Offenlegungsschrift No. 2,056,740), are also known. The fibers present in such elastomers are said to have reinforcing effects. The use of organic reinforcing fibers is described in German Offenlegungsschriften Nos. 2,220,306 and 2,164,381.
German Offenlegungsschrift No. 2,419,527 describes a process for producing decorative plastic moldings from molding compositions containing colored components. More specifically, polymer particles (for example, granulated polystyrene) which are at least partly soluble in the binder of the molding composition under molding conditions are mixed into the molding composition (for example, unsaturated polyesters containing glass fibers and/or asbestos fibers dissolved in styrene/diallyl phthalate monomers). In the disclosed process, the polymer particles differ in color from the molding composition and are processed under conditions (e.g., in the melt or by extrusion) such that the polymer particles dissolve to such a degree that a decorative effect is achieved. The particles mixed into the molding composition may be granular, flake-like or fiber-like depending upon the decorative function which they are intended to perform. The decorative effects achieved by this disclosed process are blurred color changes resembling natural stone.